The present invention relates to apparatus and methods for removing dissolved gases from liquid and for routing the removed gases to analytical instruments for analysis. More particularly, this invention is embodied in apparatus and method for extracting gases dissolved in electrical insulating oils, and for detecting and analyzing those gases.
The electric power industry has for many years recognized that certain electrical and thermal phenomena that occur in oil-insulated electrical apparatus can lead to the generation of a number of xe2x80x9cfault gases.xe2x80x9d These phenomena occur in equipment such as oil filled transformers (both oil-filled and gas-blanketed types), load tap changers, current transformers and bushings and the like. The presence of fault gases may be a measure of the condition of the equipment. As such, detection of the presence of specific fault gases in electrical apparatus, and quantification of those gases can be an important part of a preventative maintenance program.
The presence of fault gases in oil-blanketed transformers and other devices has well documented implications relating to the performance and operating safety of the transformer. There is a substantial body of knowledge available correlating the presence of gases with certain, identified transformer conditions and faults. It is therefore beneficial to monitor the condition of dielectric fluids in electric equipment as a means to maximize performance, and at the same time minimize wear and tear on the equipment, and to thereby minimize maintenance costs and down time. Thus, information relating to the presence or absence of certain fault gases in transformer oil can lead to greatly increased efficiency in the operation of the transformer.
As an example, it is known that the presence of some kinds of fault gases in transformer oil can be indicative of transformer malfunctioning, such as arcing, partial or corona discharge. These conditions can cause mineral transformer oils to decompose generating relatively large quantities of low molecular weight hydrocarbons such as methane, and some higher molecular weight gases such as ethylene and ethane. Such compounds are highly volatile, and in some instances they may accumulate in a transformer under relatively high pressure. This is a recipe for disaster. Left undetected or uncorrected, these volatile gases can lead to an increased rate of degradation, and even to catastrophic explosion of the transformer. Transformer failure is a significantly expensive event for an electric utility, not only in terms of down time and the costs of replacement equipment, but also in terms of the costs associated with lost power transmission. On the other hand, by closely monitoring dissolved gases in transformer oil, the most efficient operating conditions for a given transformer can be actively monitored and the transformer load may be run at or near a maximized peak. Moreover, when dangerous operating conditions are detected the transformer can be taken off line for maintenance.
Despite the known need for reliable equipment to monitor gas in oil, designing equipment has been problematic for a variety of reasons. There have been many attempts to solve the problems associated with transformer gas-in-oil monitoring, but none of them ideal. Some electrical utilities routinely sample transformer oil in the field, extract gas sample aliquots and return the samples to laboratories to run dissolved gas analysis, often with laboratory GCs. Sometimes portable field GCs can be used, as well. But these methods do not give real-time analysis and may result in data that is not a true measure of actual, ongoing operating conditions. Moreover, physical sampling cannot be done on a continuous, ongoing basis, and instead requires scheduled visits. Sample analysis and historical data are thus based on widely intermittent sampling protocols rather than continuous sampling. But an intermittent sampling protocol may entirely miss a substantial transient transformer fault. That is, it is unlikely that the timing of an intermittent sampling will correlate with a specific fault event. Moreover, it is well known that each transformer tends to have a unique set of operating conditions and tends to run under certain conditions unique to that transformer. In essence, each transformer has a set of normal operating conditions that are unique to that unit. Knowledge of a transformer""s normal operating conditions allows for accurate prediction and analysis of when a certain out-of-normal condition is a true fault condition or an event that might be expected. With periodic sampling it is all but impossible to develop an accurate operating profile for each transformer.
One practical result of such difficulties in such sampling and other factors has been that, out of safety and maintenance concerns, many commercial power transformers are run at loads that are significantly less than the transformer is capable of handling. Alternately, transformers are run at loads closer to their operating maximum without sufficient information about the existence of possible dangerous conditions, which could lead to catastrophic failure. This protocol for operating transformers is inefficient, expensive and in some cases dangerous.
Mechanical/vacuum and membrane extraction methods and apparatus for degassing transformer oil are also well known in the art. As one example, U.S. Pat. No. 5,659,126 discloses a method of sampling headspace gas in an electrical transformer, analyzing such gases according to a temperature and pressure dependent gas partition function, and based on the derived analysis predicting specific transformer faults. An example of a gas extraction apparatus that relies upon a membrane for extraction of gas from transformer oil is disclosed in U.S. Pat. No. 4,112,737. There, a probe having a plurality of membrane tubes is inserted directly into transformer oil in the transformer housing. The material used for the membrane is impermeable to oil, but gases dissolved in the oil permeate through the membrane into the hollow interior of the tubes. A portable analytical device such as a portable gas chromatograph is temporarily connected to the probe so that the test sample is swept from the probe into the analytical device for analysis.
Although these devices have provided benefits, there are numerous practical problems remaining to the development of reliable apparatus for extraction, monitoring and analysis of fault gases in transformer oils. Many of these problems relate to the design of reliable fluid routing systems that are redundant enough to provide a relatively maintenance free unit. Since transformers are often located in exceedingly harsh environmental conditions, fluid routing problems are magnified. This is especially true given that the instruments needed to reliably analyze the gases are complex analytical instruments.
Many chemical analytical instruments rely upon controlled and accurate fluid flow through the instrument during analytical processing. Such instruments include machines designed to perform chemical analysis of various types, purify samples and to perform monitoring of various aspects of laboratory and commercial processing. To name just a few of the types of analytical instruments in which precise fluid flow is a critical part of the functioning of the machines, there are gas chromatographs (GCs) of numerous types, spectrophotometers of many kinds, and many other similar instruments. Gas chromatographs, for example, rely upon accurate control and processing of known quantities of fluid flowing through separation columns during the analytical processing. Without accurate control of fluid flow, analytical results are compromised.
In a GC the fluid is in the form of gas. Samples of fluid under test are typically under the control of control devices such as pumps, valves, pressure transducers and pressure regulators. The control devices help in the acquisition of samples, and the isolation, handling and separation of the samples during the process of chemical analysis. In a GC, a sample aliquot is directed, either manually or automatically, through a complicated array of plumbing hardware and control systems that that perform various functions before the sample flows through one or more separation columns. In the separation columns different compounds in the sample fluid are isolated. As the isolated compounds flow out of the columns they flow through detectors of various kinds that assist in identifying and quantifying the compounds.
As a sample flows through an instrument such as a GC it may be exposed to various other fluids such as carrier fluids, calibration fluids and the like. Moreover, the fluid flow paths include many junctions and intersections. At each step along the processing path where fluids are rerouted or further isolated, the fluid flows through a variety of plumbing hardware and control systems.
It is obvious that in many analytical instruments that require controlled fluid flow there are numerous fluid flow paths, and complex hardware systems that include tubing, barbs, couplings, valves, sensors, pumps and regulators of various kinds. The plumbing systems in even relatively simple instruments such as some gas chromatographs can become exceedingly complicated, not to mention the complexity added by the fluid control systems.
Precision, reliability and accuracy are of course primary goals of any analytical analysis. As such, it is essential in an analytical instrument to eliminate, or at least minimize, all sources of system failure, including problems such as leaking fittings that can adversely effect the analytical processing. The complexity of the plumbing and fluid controlling hardware of many analytical instruments presents a situation that is at odds with the fundamental principles of accuracy and precision that such instruments rely upon. Accurate analytical results require accurate fluid processing, without system failures such as non-fluid-tight couplings. But every fitting, connection, interconnection and fluid-controlling device in an analytical instrument introduces a potential site for a problem such as a leak. When even a small leak occurs in a critical connection the accuracy of analytical test data is compromised. In an instrument that contains dozens of couplings and connections the opportunity for incorrectly connected fittings is multiplied many times over.
The problems described above with respect to complicated fluid connections are well known to any laboratory technician who has operated an analytical instrument such as those described. Even in the relatively idealized conditions of a modern laboratory, and even with laboratory grade instruments, plumbing problems are a constant source of trouble with analytical instruments such as GCs. As such, there is a great benefit in reducing the number and complexity of fittings in an instrument that uses fluid flow.
But the problems noted above are even more pronounced with analytical instruments that are designed for use in the field rather than in a controlled laboratory environment. There are several reasons. First, field instruments tend to be smaller since portability may be a primary goal. As the instruments get smaller so do the fittings and connections. With miniaturized-hardware it is more difficult to ensure fluid-tight processing. Second, an instrument designed for use in the field is often subject to more extreme environmental conditions and rougher handling. In many respects, therefore, field units need to be even more robust than their laboratory counterparts. This can be a difficult objective when another goal in designing the unit is reduction of size.
A relatively newer type of analytical instrument is an in-situ monitoring device that is installed in place to monitor on an ongoing basis some kind of processing activity. Such devices are often designed to interface with telephony equipment for automatic transmission of analytical data and for remote access to central processing units in the instruments. These devices may be left in the field for extended periods of time, and do not have the benefit of the constant monitoring and maintenance that both laboratory and portable instruments might enjoy. In-situ instruments therefore must be extremely rugged to provide reliable data over an extended period of time.
In-situ instruments also may be placed in extreme environmental conditions that test the limits of hardware design. For instance, such devices may be subjected to wide fluctuations in ambient temperature and other extremes in weather conditions, and to harsh chemical environments. Design engineering must take these conditions into account. But in instruments that include complicated plumbing schemes it is even more difficult than in laboratories to minimize chances for leaking fittings and the accompanying errors in obtaining reliable data.
There have been various attempts made at developing in-situ analytical instruments for continuous monitoring and analysis of dissolved gas in transformer oil. Some of these attempts have shown some promise of success. Others have not fared as well. Regardless, the in-situ analytical instruments are often subjected to extremely harsh environmental conditions. For example, as noted, power transformers may be located in areas where ambient temperatures vary from extreme cold in winter months to extreme heat in summer. Furthermore, all large transformers are prone to vibration during operation that can be significant. Such vibration on a continued basis can be very rough on equipment near the transformer. All things considered, it is very difficult to design an accurate, precise and rugged analytical instrument that can withstand these environmental conditions without repeated failures.
The problems described above with complicated plumbing, control and hardware systems are amplified many times over in the extreme conditions found at transformer locations. The extreme temperature variations can cause thermal expansion and contraction that leads to leaking fittings and other connections, and environmental vibrations can, over time, loosen fittings and damage sensitive connections.
Therefore, despite advances in the technological solutions surrounding analytical instruments designed to sample, analyze and report data from remote locations, there is a need for a fluid handling system that is rugged and redundant enough that it will function without failure and without regular maintenance. Such a fluid handling system would be advantageously and beneficially used in both field instruments and in laboratory grade instruments.
While there are many different approaches to the actual degassing of oil from electric power transmission equipment, any in-situ approach must be designed to ensure fluid-tight processing. This is important for several reasons. First, failure of an oil transfer line can lead to transformer insulating oil escaping from the transformer. Left undetected, loss of oil can lead to transformer failure. Leaking oil is also an environmental concern. Second, an analytical system that introduces gases from the analytical instrument to the transformer creates problems independent of transformer performance, and is unacceptable. These problems are particularly difficult with regard to the fluid connections associated with the degassing apparatus, whether located within the transformer or adjacent to it.
The advantages of the present invention are achieved in a first preferred embodiment of a gas extraction apparatus that provides for accurate extraction of dissolved gases and for fluid-tight handling of both oil and extracted gas. The apparatus utilizes an extraction module comprising plural composite hollow fiber tubes coated with a thin layer of a non-porous gas permeable polymer, making each tube gas, but not dielectric fluid permeable. The extraction module is contained within a fluid-tight cartridge housing. The apparatus includes and is plumbed to an analytical instrument such as a gas chromatograph that utilizes a ported manifold for routing and controlling fluid flow into and through the instrument. The ported manifold includes isolated fluid flow paths that eliminate plural fittings and hardware plumbing devices. The manifold is mated to a cooperatively ported collar or flange, which is designed to mate with a rotary injector valve. Fluid control apparatus such as pressure transducers, valves and pressure regulators are connected directly to the ported manifold and are fluidly connected with appropriate fluid streams in the manifold. The combination of the manifold and collar and the manner in which the collar mates with the rotary injector valve provides for a rugged and redundant fluid flow system that eliminates the vast majority of fittings normally found in analytical instruments.